Poor 420

[bluepain]

Hi guys need a little help, I've been getting error code PO420 for ages now ,
And gotta say it's getting to me.
I've had coils and plugs relaced, it ran a lot smoother but fault code came back after 300 mls,
Had rear O2 sensor changed code came back after 30 mls
Had front O2 sensor changed,guess what code came back
Garage informed me it must be the manifold cat, had the BMW part changed £800 just for the parts,cats are integrated into manifold making them dammit expensive
Any way fault dissapered.
Yes theres a but....
Fault has started to returning after about 500 mls.
Engine runs smoothly without miss fire, and passes MOT emissions limits for this model 2.0l I sport.
I read from a previous postings ,I'm not the first to have this problem,and that the valveatronic engine is a needy child..
I did read theres an oil pump that can leak situated at the rear of the block,but I can't find it..
Any help would be appreciated .
Cheers

 

[mac27040]

found this on an old thread

Most common with the older engines was the tendency for the upper chain guard to snap which caused rough running and sometimes timing issues. The quick fix was to fit an upgraded chain tensioner (cheap and easy) which often helped. These engines also use a vacuum pump at the back of the block which can leak and cause the same issues you describe. The vacuum pump is easy enough to access and is worth looking at.

I expect you'll find you have some sort of leak somewhere. Whipping off the rocker cover gasket will reveal the upper chain guard and you can check the chain tension to see if that needs looking at.